tests/docker: add test-misc for building tools & docs

Add yet another test type so we cna quickly exercise the miscellaneous
build products of the build system under various docer configurations.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>

tests/docker/test-misc

+#!/bin/bash -e
+#
+# Build the miscellaneous components
+#
+# Copyright (c) 2019 Linaro Ltd.
+#
+# Authors:
+#  Alex Bennée <alex.bennee@linaro.org>
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or later.
+# See the COPYING file in the top-level directory.
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+. common.rc
+
+cd "$BUILD_DIR"
+
+# build everything else but QEMU
+configure_qemu --disable-user --disable-system --enable-docs --enable-tools
+build_qemu
+install_qemu